In an electrophotographic apparatus, a contact charging method is used in many cases in which a roller-shaped charging member (hereinafter referred to as “charging roller”) is brought into contact with an electrophotographic photosensitive member, and only a direct current voltage, (hereinafter referred to as “DC charging method”) or a superposed voltage of a direct current voltage and an alternating current voltage (hereinafter referred to as “AC+DC superposed charging method”) is applied to charge the electrophotographic photosensitive member.
The DC charging method is preferably used in view of low cost and reduction in size of apparatus. However, compared with the AC+DC superposed charging method, the DC charging method has a narrow discharge region and cannot obtain an effect of uniforming a charged potential by an AC discharge current. Therefore, when only a direct current voltage is applied between a charging member having a locally uneven resistance on its surface and an electrophotographic photosensitive member, nonuniformity is generated in surface charge of the electrophotographic photosensitive member due to the uneven resistance, and as a result, density nonuniformity in the form of transverse streaks may be generated in an electrophotographic image in some cases.
In PTL 1, in order to overcome the above problem, a technique has been disclosed in which insulating particles are contained in a surface layer of a charging member to form convex portions derived from the insulating particles.